By reason of the rapid development of new and improved nuclear power plant types, it becomes increasingly necessary to dispose of previously-built experimental reactors and out-of-date nuclear power plants. A particular problem in disposing of nuclear power plants and nuclear reactors arises out of the fact that the reactor parts contain radioactive material and particularly radioactively contaminated water which must not escape during the demolishing nor endanger the people performing the demolishing. When sawing up the reactor part or demolishing it in some other way for disposal, catching the radio-actively contamnated water and protecting the surroundings from the radioactive material constitutes a practically insoluble problem.